Digital signatures are vital for maintaining the authenticity and integrity of PDF documents. They provide a reliable way to verify the signer's identity and ensure that the document's content has not been tampered with since the signature was applied. By using digital signatures, you can enhance the security and trustworthiness of your documents. In this article, we will explore how to add and remove digital signatures in PDF files in Python using Spire.PDF for Python.

• Add a Digital Signature to PDF in Python
• Add an Invisible Digital Signature to PDF in Python
• Remove Digital Signature from PDF in Python

Install Spire.PDF for Python

This scenario requires Spire.PDF for Python and plum-dispatch v1.7.4. They can be easily installed in your Windows through the following pip command.

pip install Spire.PDF

If you are unsure how to install, please refer to this tutorial: How to Install Spire.PDF for Python on Windows

Add a Digital Signature to PDF in Python

You can use the PdfOrdinarySignatureMaker.MakeSignature(sigFieldName: str, page: PdfPageBase, x: float, y: float, width: float, height: float, signatureAppearance: IPdfSignatureAppearance) method to add a visible digital signature with a custom appearance to a specific page of a PDF document. The detailed steps are as follows.

• Create a PdfDocument instance.
• Load a PDF document using PdfDocument.LoadFromFile() method.
• Create a PdfOrdinarySignatureMaker instance and pass the PdfDocument object, certificate (.pfx) file path and certificate password to the class instructor as parameters.
• Set signature details, such as the signer’s name, contact information, location, and signature reason, using the properties of the PdfOrdinarySignatureMaker class.
• Create a PdfSignatureAppearance instance for the signature, and then customize the labels for the signature and set the signature image.
• Get a specific page in the PDF document using PdfDocument.Pages[] property.
• Call the PdfOrdinarySignatureMaker.MakeSignature(sigFieldName: str, page: PdfPageBase, x: float, y: float, width: float, height: float, signatureAppearance: IPdfSignatureAppearance) method to add the digital signature to a specific location of the page.
• Save the result document using the PdfDocument.SaveToFile() method.

from spire.pdf.common import *
from spire.pdf import *

# Create a PdfDocument instance
doc = PdfDocument()
# Load a PDF file
doc.LoadFromFile("Sample.pdf")

# Create a signature maker
signatureMaker = PdfOrdinarySignatureMaker(doc, "gary.pfx", "e-iceblue")

# Configure the signature properties like the signer's name, contact information, location and signature reason
signature = signatureMaker.Signature
signature.Name = "Gary"
signature.ContactInfo = "+86 12345678"
signature.Location = "China"
signature.Reason = "I am the author."

# Create a custom signature appearance
appearance = PdfSignatureAppearance(signature)
# Set label for the signer's name
appearance.NameLabel = "Signer: "
# Set label for the contact information
appearance.ContactInfoLabel = "Phone: "
# Set label for the location
appearance.LocationLabel = "Location: "
# Set label for the signature reason
appearance.ReasonLabel = "Reason: "
# Set signature image
appearance.SignatureImage = PdfImage.FromFile("SigImg.png")
# Set the graphic render/display mode for the signature
appearance.GraphicMode = GraphicMode.SignImageAndSignDetail
# Set the layout for the signature image
appearance.SignImageLayout = SignImageLayout.none

# Get the first page
page = doc.Pages[0]

# Add the signature to a specified location of the page
signatureMaker.MakeSignature("Signature by Gary", page, 90.0, 600.0, 260.0, 100.0, appearance)

# Save the signed document
doc.SaveToFile("Signed.pdf")
doc.Close()

Add an Invisible Digital Signature to PDF in Python

An invisible signature in a PDF is a type of digital signature that provides all the security and authentication benefits of a standard digital signature but does not appear visibly on the document itself. Using the PdfOrdinarySignatureMaker.MakeSignature(sigFieldName: str) method of Spire.PDF for Python, you can add an invisible digital signature to a PDF document. The detailed steps are as follows.

• Create a PdfDocument instance.
• Load a PDF document using PdfDocument.LoadFromFile() method.
• Create a PdfOrdinarySignatureMaker instance and pass the PdfDocument object, certificate (.pfx) file path and password to the class instructor as parameters.
• Add an invisible digital signature to a PDF document using the PdfOrdinarySignatureMaker.MakeSignature(sigFieldName: str) method
• Save the result document using the PdfDocument.SaveToFile() method.

from spire.pdf.common import *
from spire.pdf import *

# Create a PdfDocument instance
doc = PdfDocument()
# Load a PDF document
doc.LoadFromFile("test2.pdf")

# Create a signature maker
signatureMaker = PdfOrdinarySignatureMaker(doc, "gary.pfx", "e-iceblue")

# Add an invisible signature to the document
signatureMaker.MakeSignature("Signature by Gary")

# Save the signed document
doc.SaveToFile("InvisibleSignature.pdf")
doc.Close()

Remove Digital Signature from PDF in Python

To remove digital signatures from a PDF document, you need to iterate through all form fields in the document, find the form fields that are of PdfSignatureFieldWidget type and then remove them from the document. The detailed steps are as follows.

• Create a PdfDocument instance.
• Load a PDF document using PdfDocument.LoadFromFile() method.
• Get the form field collection of the document using PdfDocument.Form property.
• Iterate through the form fields in the collection from the last to the first.
• Check if the field is a PdfSignatureFieldWidget object.
• If the result is True, remove the field from the document using PdfFormFieldWidgetCollection.FieldsWidget.RemoveAt(index) method.
• Save the result document using the PdfDocument.SaveToFile() method.

from spire.pdf.common import *
from spire.pdf import *

# Create a PdfDocument instance
doc = PdfDocument()
# Load a PDF document
doc.LoadFromFile("Signed.pdf")

# Get form field collection from the document
pdfForm = doc.Form
formWidget = PdfFormWidget(pdfForm)

# Check if there are any form fields in the collection
if formWidget.FieldsWidget.Count > 0:
    # Loop through all form fields from the last to the first
    for i in range(formWidget.FieldsWidget.Count - 1, -1, -1):
        field = formWidget.FieldsWidget[i]    
        # Check if the field is a PdfSignatureFieldWidget
        if isinstance(field, PdfSignatureFieldWidget):
            # Remove the field
            formWidget.FieldsWidget.RemoveAt(i)

# Save the document
doc.SaveToFile("RemoveSignature.pdf")
doc.Close()

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